Am sure Apple is already working on iOS 12 beta 4 and/or 5 - that's the way software releases are managed.
Here at the company I am working at we usually have a code-freeze (internal testing phase/no further code changes!) 4 weeks ahead of the public release which in my case means go live for all real customers.
In the meantime (freeze period) the next releases are already under development at the same time.
If there is a HUGE issue popping up code fixing is also permitted during the freeze, small issues are postponed for following releases.
If the GPS-issue (which seems to occur for some but not all beta testers) is considered as socalled HUGE issue by Apple, I am sure Apple might implement the GPS-fix from beta 3 or 4 into the public beta build.
If not, no problem
- Betas should only be deployed on iOS devices dedicated for software development respectively not on your main device.